US10714238B2 - Joint for superconducting wire - Google Patents

Joint for superconducting wire Download PDF

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Publication number
US10714238B2
US10714238B2 US15/544,678 US201615544678A US10714238B2 US 10714238 B2 US10714238 B2 US 10714238B2 US 201615544678 A US201615544678 A US 201615544678A US 10714238 B2 US10714238 B2 US 10714238B2
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sintered body
joint
superconducting wires
mgb
wire
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US20180012682A1 (en
Inventor
Yota ICHIKI
Tsuyoshi Wakuda
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Hitachi Ltd
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Hitachi Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B12/00—Superconductive or hyperconductive conductors, cables, or transmission lines
    • H01B12/02—Superconductive or hyperconductive conductors, cables, or transmission lines characterised by their form
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
    • H01R4/00—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation
    • H01R4/58—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation characterised by the form or material of the contacting members
    • H01R4/68—Connections to or between superconductive connectors
    • H01L39/02—
    • H01L39/141—
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
    • H01R4/00—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation
    • H01R4/28—Clamped connections, spring connections
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/20—Permanent superconducting devices
    • H10N60/202—Permanent superconducting devices comprising metal borides, e.g. MgB2
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/80—Constructional details

Definitions

  • the present invention relates to a joint structure of a joint for superconducting wires using magnesium diboride (MgB 2 ).
  • the persistent current mode is an operation method in which a current is continuously flown in a closed circuit formed by using a superconductor. That is, since a superconducting wire has a resistance of zero, once a current is flown in a closed circuit, the current is continuously flown without attenuation.
  • a technique to joint end parts of superconducting coils or superconducting wires constituting a persistent current switch with a superconductor is important.
  • superconducting wires are generally used as multi-core wires constituted by a plurality of filaments in view of current capacity, wire length, magnetic stability and alternate current loss, and thus are demanded to be capable of joint multi-core wires.
  • PTL 1 describes a method including polishing tip ends of wires containing a mixed powder of magnesium (Mg) and boron (B) or MgB 2 wires to expose MgB 2 cores, inserting the wires in a container, filling the container with a mixed powder of Mg and B from the direction orthogonal to the wires, pressurizing the mixed powder, and conducting a heat treatment. By the heat treatment, a sintered body of MgB 2 is formed, and the wires are jointed.
  • Mg magnesium
  • B boron
  • the cores of the tip end parts of the wires (MgB 2 , or a mixed powder containing Mg and B) are exposed in the metal container and are jointed through the MgB 2 sintered body.
  • MgB 2 the cores of the tip end parts of the wires
  • a mixed powder containing Mg and B the cores of the tip end parts of the wires
  • the problem in jointing multi-core wires is fixing of filaments (these refer to single core wires constituting a multi-core wire) in a joint process.
  • the methods are a twisted wire method in which single core wires are each subjected to a wire drawing processing so that the single core wires become thin to a final wire diameter, and then the single core wires are twisted, and an composite wire method in which a plurality of single core wires that have been subjected to a wire drawing processing halfway are composed in a pipe, and the pipe is further subjected to a wire drawing processing.
  • constitutional materials of a superconducting wire contain Cu (or a Cu alloy) for electrical and thermal stabilization, but when superconducting wires are jointed by a MgB 2 sintered body, Mg reacts with Cu. Therefore, in general, it is necessary to dissolve Cu by a chemical polisher and remove Cu. Therefore, in either of the twisted wire method and composite wire method, it is necessary that filaments each constituted by a MgB 2 core and a barrier material surrounding the core (Fe, Nb and the like) are jointed in a scattered state. In jointing the filaments, it is necessary to expose the MgB 2 cores by polishing, but it is highly possible that thin filaments (generally having a wire diameter of about several hundred micrometers) are damaged.
  • the object of the present invention is to solve the above-mentioned problem relating to the joint of MgB 2 multi-core wires to thereby attain a joint having a high critical current property without damaging filaments of multi-core wires.
  • the present inventors considered so as to solve the above-mentioned problem, and consequently found that the above-mentioned problem can be solved by a method for treating end parts of a multi-core wire, and completed the present invention.
  • the joint for superconducting wires according to the present invention has a MgB 2 sintered body for mechanically fixing filaments besides a MgB 2 sintered body that contributes to an electric joint.
  • a joint having a high critical current property can be attained without damaging filaments of multi-core wires.
  • FIG. 1 is a constitutional example of a superconducting magnet.
  • FIG. 2 shows a step for pre-treating a multi-core twisted wire.
  • FIG. 3 shows a step of forming an MgB 2 sintered body.
  • FIG. 4 shows the structure of the multi-core MgB 2 wire after the heat treatment.
  • FIG. 7 shows structure ( 1 ) of a joint for superconducting wires.
  • FIG. 8 shows structure ( 2 ) of a joint for superconducting wires.
  • Magnesium diboride (MgB 2 ) has a higher critical temperature at which it transits to superconductive than the critical temperatures of conventional metal-based materials, and thus practical use of magnesium diboride as a superconducting magnet by cooling in a refrigerator without using liquid helium is expected. Since operating at 10 K or more is required in such case, conventional superconducting solder joint in which the critical temperature is 10 K or less cannot be applied. Therefore, it is necessary to establish a technique for jointing MgB 2 wires by MgB 2 .
  • FIG. 1 shows a constitutional example of the superconducting magnet.
  • the superconducting magnet of FIG. 1 includes a cryostat 26 in which a superconducting coil 22 and a persistent current switch 23 are disposed, and these are cooled by a refrigerator, which is not illustrated, through a support plate 25 .
  • a current is fed through a current lead 24 that connects a power source, which is not illustrated, at the side of room temperature, and the superconducting coil 22 at a low temperature side.
  • the superconducting joint 21 is disposed on two portions between the superconducting coil 22 and the persistent current switch 23 .
  • Multi-core twisted wires having seven twisted single core wires (filaments) each having a MgB 2 core in a metal sheath are explained here as an example of superconducting wires to be jointed.
  • a metal sheath is generally constituted by a stabilizing material for ensuring high electric and thermal stability such as copper, and a barrier material for preventing a reaction with the stabilizing material during a heat treatment for converting Mg and B to MgB 2 .
  • the number of the cores in each wire is not limited to seven (single core wires are also encompassed).
  • FIGS. 2 to 5 show the steps of the treatment of the wire end parts in this Example.
  • the wire cores may already be in an MgB 2 state (calcination has been completed).
  • wires in an MgB 2 state are mechanically brittle, it is desirable that the wires are in a state of Mg+B (uncalcined).
  • FIG. 3 shows the steps of forming a MgB 2 sintered body.
  • seven filaments are fixed with a raw material powder for a first MgB 2 sintered body in a wire support element 5 .
  • FIG. 3 is a drawing seen from the direction of the tip ends of the wires.
  • FIG. 3 central drawing
  • seven filaments each constituted by a wire core 7 and a barrier material 4 before calcination are lined transversely.
  • the mixed powder 6 of Mg and B is further laminated on the filaments and pressurized.
  • the seven filaments are lined in one layer here, the filaments may be lined in two layers by dividing the filaments, for example, into four and three filaments.
  • it is desirable that the length of the wire end parts to be fixed is longish with consideration for the case when the joint fails and is done again. Subsequently, a heat treatment for converting to MgB 2 is conducted. In the steps of FIG.
  • the wire cores 7 are in an uncalcined state, and thus are converted to MgB 2 simultaneously with the heat treatment at this time.
  • the wire cores 7 that have been calcined are used in the steps of FIG. 3 , it is also possible to subject only the end parts to a local heat treatment.
  • the heat treatment is generally conducted by using an electric furnace in an inert gas such as argon or nitrogen at 600° C. to 800° C. Since the electrical property of the MgB 2 sintered body for fixing the wire end parts is not questioned, the calcination may be conducted under heat treatment conditions at which the critical current property of the wires is maximum.
  • FIG. 5 shows the structure of the multi-core MgB 2 wire after the polishing.
  • FIG. 5 (upper drawing) shows an upper surface view of the wire end parts after the polishing
  • FIG. 5 (lower drawing) shows a cross-sectional view.
  • the polishing method may be general mechanical polishing. It is desirable that the angle of the polished surface with respect to the length direction of the wires is a small angle with consideration for the surface area of the wire cores 9 to be exposed, but if the angle is small, necessary space and amount of substance increase. Therefore, the angle is suitably from 10° to 30°.
  • FIG. 6 is another example of the structure of the multi-core MgB 2 wires after the polishing.
  • the case when two multi-core wires are fixed in the same sintered body is shown.
  • the two multi-core wires to be jointed can be fixed by the same sintered body as shown in FIG. 6 .
  • FIG. 7 shows joint ( 1 ) for superconducting wires. This is a joint in the case when two multi-core wires are inserted from the same direction and lined transversely, and another wire is present in the depth direction of the plane of paper besides the wire shown in the drawing.
  • the transversely refers to
  • FIG. 8 shows joint ( 2 ) for superconducting wires. This is a joint in the case when two multi-core wires are inserted from the opposing directions.
  • FIG. 9 shows joint ( 3 ) for long electrical transmission wires. This is a joint in the case when two multi-core wires are inserted from the same direction and lined vertically, and insertion from the opposing directions as shown in, insertion from the same direction with lining vertically as shown in FIG. 9 , and the like can be considered.
  • the MgB 2 sintered body 8 is positioned by surrounding the outer peripheries of the wires each constituted by the wire core 9 and the barrier material 4 .
  • the MgB 2 sintered body 10 is positioned along a polished surface constituted by the wire cores 9 and the barrier material 4 and the MgB 2 sintered body 8 . Therefore, there are both a part in which the MgB 2 sintered body 8 and the MgB 2 sintered body 10 are disposed in a side-by-side relation, and a part in which the MgB 2 sintered body 8 and the wire are disposed in a side-by-side relation.

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Superconductors And Manufacturing Methods Therefor (AREA)
US15/544,678 2015-03-10 2016-02-03 Joint for superconducting wire Active 2037-05-02 US10714238B2 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP2015-046620 2015-03-10
JP2015046620 2015-03-10
PCT/JP2016/053127 WO2016143416A1 (ja) 2015-03-10 2016-02-03 超電導線材の接続部

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US20180012682A1 US20180012682A1 (en) 2018-01-11
US10714238B2 true US10714238B2 (en) 2020-07-14

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JP (1) JP6442598B2 (ja)
WO (1) WO2016143416A1 (ja)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11101215B2 (en) * 2018-09-19 2021-08-24 PsiQuantum Corp. Tapered connectors for superconductor circuits
JP7351771B2 (ja) * 2020-03-02 2023-09-27 株式会社日立製作所 超電導線材の接続部および超電導線材の接続方法
JP7428617B2 (ja) * 2020-09-03 2024-02-06 株式会社日立製作所 超電導線材の接続部および超電導線材の接続方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003002483A1 (fr) 2001-06-29 2003-01-09 International Superconductivity Technology Center, The Juridical Foundation Procede de jonction d'oxyde supraconducteur et corps a cet effet
US20120108435A1 (en) 2010-10-28 2012-05-03 Hitachi, Ltd. Joint of superconducting wires and method for joining superconducting wires
WO2013161475A1 (ja) 2012-04-23 2013-10-31 株式会社 日立製作所 ＭｇＢ2超電導マグネット
WO2015015627A1 (ja) 2013-08-02 2015-02-05 株式会社 日立製作所 超電導マグネット及びその製造方法

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003002483A1 (fr) 2001-06-29 2003-01-09 International Superconductivity Technology Center, The Juridical Foundation Procede de jonction d'oxyde supraconducteur et corps a cet effet
US20030148891A1 (en) 2001-06-29 2003-08-07 Kazumasa Iida Method of joining oxide superconductors and oxide superconductor joiner
US20120108435A1 (en) 2010-10-28 2012-05-03 Hitachi, Ltd. Joint of superconducting wires and method for joining superconducting wires
JP2012094413A (ja) 2010-10-28 2012-05-17 Hitachi Ltd 超電導線材の接続部及び超電導線材の接続方法
WO2013161475A1 (ja) 2012-04-23 2013-10-31 株式会社 日立製作所 ＭｇＢ2超電導マグネット
WO2015015627A1 (ja) 2013-08-02 2015-02-05 株式会社 日立製作所 超電導マグネット及びその製造方法

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
International Search Report dated Apr. 19, 2016 as issued in International Application No. PCT/JP2016/053127.

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Publication number Publication date
JP6442598B2 (ja) 2018-12-19
US20180012682A1 (en) 2018-01-11
JPWO2016143416A1 (ja) 2017-10-19
WO2016143416A1 (ja) 2016-09-15

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